CE-201Lecture 2-3

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INDIANINSTITUTEOFTECHNOLOGYROORKEE

DEPARTMENT

OF

CIVIL

ENGINEERING

CE201:ComputerAidedGraphicsWeek2&3,WedAug13,20

RajatRastogi

ra atfce iitr.ernet.in

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Graphics,sketching,photography

en er ng, o e ngan n ma on

ApplicationsofCGMovies,Games,Entertainment,CAD,Art,

Interactivegraphics,Education,Training,

sua za on, es gn ng AdvancementinGPUs

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Random/Rasterscan

Co ourMo e s

Pixels DisplayDevices

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VideoDisplayTechnologiesAugust18,2008 4RajatRastogi

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Extremelyhighvoltage

Electrongun

FocusinganddeflectionsystemsPhosphorcoatedscreen

Glasstubeenvelopemaintaining


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Intensit oftheelectronbeamiscontrolledb settin volta e

levelonthecontrolgrid.Negativevoltagewilldecreasethenumberofelectronspassingthrough.

s e s ance rave e ya eam ncreases owar s eperipheryofthescreen,duetoitscurvature,displayedimage

becomeblurred.

Deflectionoftheelectronbeamcanbecontrolledeitherwithelectricfieldorwithmagneticfield.

ectronstrans erenergytop osp or,w c exc tesan onheatinggiveslightenergyproducingglowingspot,which

fadesasphosphorreturnsbacktogroundenergylevel.


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Thefrequencyorcolor

thephosphoris

proportionaltothe

energy erencebetweentheexcited

quantumstateandthe


groundstate.

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Phosphorsaredefinedeitherbycolour ortheirpersistence(howlongtheycontinuetoemitlight).

Persistence isdefinedastimeittakestheemittedlightfromthescreentodecaytoonetenthofitsoriginalintensity.

Phosphorwithlowerpersistenceisusefulforanimation;andwithhigherpersistenceisusefulforhighlycomplex,staticpictures.

Usualpersistencerangeforgraphicmonitorsis10to60microseconds.

Resolution ofCRTisdefinedasmaximumnumberofpointspercentimeterthatcanbeplottedhorizontallyorvertically.


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Resolution:

Twoilluminatedphosphorspotsaredistinguishablewhentheirseparationisgreaterthanthediameteratw c aspo n ens y as a en o percen o maximum

De endentu on Typeofphosphor

Intensitytobedisplayed

Highdefinitionsystem:basicallyhighresolutionsystem,1280x1024orhigher


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AspectRatio:

Ratio

of

vertical

points

to

horizontal

points

necessary

toproduceequallengthlinesinbothdirectionsonthescreen.

Ex.meanslengthof3pointsonverticalline=length

of

4

points

on

horizontal

line

Sizeoftube(=lengthofscreendiagonal)Brightnessofphosphorsvs.darknessoftube

SpeedofelectrongunWidthofelectronbeamPixels


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DVSTstoresthe ictureinformationasachar e

distributionjustbehindthephosphorcoatedscreen. Itusestwoelectronguns,primarygunstorespicture

patternandfloodgunmaintainspicturedisplay.

Thereisnoneedtorefreshscreen,henceverycomplexp c urescan e sp aye a very g reso u ons

withoutflicker.

,beerasedandthewholepictureistobeerasedand

redrawn.Nowreplacedbyrastersystems.


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PlasmaPanels

Liqui crysta isp ays

Twocategories Emissivedisplays:devicesthatconvertelectricalenergy

intolight.Ex.Plasmapanel,thinfilm

electroluminescent dis la s li htemittin diodes

Nonemissiveorreflectivedisplays:useopticaleffectstoconvertlightfromasourceintographicpatterns.Ex.

LCD


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Alsocalled asdischar edis la s constructedb fillin a

mixtureofgas(usuallyhasneon)betweentwoglassplates.

ThegasisexcitedbyelectricfieldemittingUVlight.

UVlightexcitesphorphor.

Phosphorrelaxesandemitssomeothercolour

Gas at intersection of hori. andvert. conductors break down onapplication of high voltage into


ions

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OLEDsfunctionlikeregularsemiconductorLEDs

Thinfilmdepositionoforganic,light

emittingmoleculesthroughvapor

sublimationinavacuum.

Dopeemissivelayerswithfluorescent.


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thatliquefywhenexcitedbyheatorEfield Cr stallinestatetwists olarizedli ht90

Flatpaneldisplayscommonlyusenematic

(threadlike)liquidcrystalcompounds

Itconsistsof

Liquidcrystals

Glassplates 2

Lightpolarizer 2at90o

Transparentconductors builtintoglassplatesat90o


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matrix


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Spaceball

Trackball


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Alsocalledvectororstrokewritingorcalligraphicdisplays Earlycomputerdisplays:basicallyanoscilloscope Refreshdisplayfileorbufferorlistorprogramme,a

memor area stores a set of line drawin commands.

Thesehavehigherresolutionthanrasterscansystems.

Lines

drawn

are

smoother

in

contrast

to

raster

system,

, .

Penplotterisanexampleofrandomscan,hardcopydevice.

sa vantages: Justdoeswireframe,likelinedrawingapplications Complexscenescause visibleflicker


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screenwhereapictureistobedrawn .


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Pixel:Onedotorpictureelement(pel)ofthe

Scan

line:

A

row

of

pixels


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,

onerowatatimefromtoptobottom.Asthe

,

beamintensityisturnedonandofftocreatea

.

Picturedefinitionisstoredinamemoryarea

.


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Theintensit ran eof ixel ositionsdefine

capability

of

raster

system.

The

frame

buffer

may

becalled:

Bitmap:withonebitperpixel,ex.Blackandwhitesystem

,definitionsystems

Refreshin onrasterscandis la iscarriedoutat

arateof60to80framespersecond(Hz).Thiscreatesnewimage.


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VerticalSyncPulse: SignalsthestartofthenextfieldVerticalRetrace: Timeneededto etfromthebottom

ofthecurrentfieldtothetopofthenextfield

HorizontalSyncPulse: Signalsthestartofthenewscanline

HorizontalRetrace: Thetimeneededtogetfromthe

en

o

e

curren

scan

ne

o

e

s ar

o

e

nex

scanline


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Assumewecanonlyscanallpixelsofentirescreenat30frames/second.Someflickerwillbenoticedhere.

Toreduceflicker,divideeachframeintotwofields

ofoddandevenlines.Thisreducesthescantimeofscreenfromtoptobottomtohalfasthebeamwill

sweepeveryalternatescanlineinonepassin1/60s.

1/30Sec 1/30Sec1/60Sec 1/60Sec 1/60Sec 1/60Sec

Field1 Field 2


Frame Frame

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Anima eiscom osedofdiscrete ixelsor icture

elements. Thesearearrangedinarowcolumnfashiontoforma

rectangulararea(raster).

The

total

number

of

pixels

in

a

image

is

a

function

of

the

s zeo e magean num ero p xe sperun eng n

thehorizontalaswellasverticaldirection(Resolution).

horizontaldirectiontimesthetotalnumberofpixelsin

theverticaldirection(512x512,640x480,1024x768).


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Sizeofima e at400 ixels erinchfor640x480ima e

640/400

x

480/400

=

1.6

x

1.2

inch Aspectratio,for640x480image=640/480=4/3

Pixelatlowerleftcornerofanimageisconsideredtobe

at

the

origin

(0,0)

of

a

pixel

coordinate

system.(639,479)(0,479)

(0,0) (639,0)


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Therearethreet esofcones,referredtoeitheras

S,M,andL,whichare

equivalenttoblue,green,

and

red

sensors,

respectively.Theirpeak

sensitivitiesarelocatedat

approximately430nm,

560nm,and610nmforthe

"average"observer


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ColourspecificationusingRBGmodelisanadditiverocess.Itstartswith G

blackandnecessary

primarycomponents GreenYellow

(0,1,0)

area e oy e

desiredcolour.

Cyan

White

, ,

(1,1,1)(0,1,1)

Grey axis

principalofdisplaymonitor. R

Black

Blue

Red(0,0,0)

0,0,1(1,0,0)


BMagenta

(1,0,1)

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Delta electron gun In-line electron gunarrangement arrangement


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plane

X+Y+Z=1

CIE Chromaticity Diagram


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Conversion from


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Thisdefinescoloursusingasubtractiveprocesses.Itstartswithwhiteanda ro riate rimar colouris

subtractedtogetdesiredcolour.

It

is

working

principal

of

printers.

1

1

and1

1

=

=

G

R

M

C

M

C

G

R

11 BYYB

Subtractive


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Four

colour

procss

or

simplyprocess.

Whenthetintsoffour

colours

are

printed

in

overlappingpatterns,it

givesillusionofprinted

.


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RGB Color Model CMYK Color Model

Additive color modelFor computer displays

Subtractive color modelFor printed material

Uses light to display color

Colors result from transmitted light

Red + Green + Blue = White

Uses ink to display color

Colors result from reflected light

Cyan + Magenta + Yellow = BlackBlack means total absence of light White means total absence of ink


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To roduceblue onehasto

cyan red blue andgreen

mixcyanandmagenta

Blackisusedtoensurehigh

magenta greenblue and

red

qua y ac pr n ng. s

representedbyK

Hence CMYK

yellow bluered and

green ImageprintedwithCMYK

modelcannotbeconvertedac a none to mo e ,ast e

informationgetslost.


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Certainspaceisallottedtoapixeltocodeits. . ,

Bit1:r Bit2:g Bit3:b Colour name0 0 0 Black

0 0 1 Blue

0 1 0 Green

0 1 1 Cyan

1 0 0 Red1 0 1 Magenta

1 1 0 Yellow


1 1 1 white

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Each

pixel

has

3

bits,

with

each

taking

either

0

or

1

to

representcolour.Itcanthuspresent2x2x2=8colours

In24bitpixel,eachprimarycolour(onebyte)has8bits.Onebyte,therefore,canpresent 2x2x2x2x2x2x2x2=256

A24bitpixelcanthushave256x256x256possiblechoices=16,777,216colourintensities.

This24bitformatiscalledtruecolourrepresentation.Highstoragespaceisrequiredforthisformat.


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The

number

of

possible

colors

would

be

2

to

the

power

of

thenumberofbitsperpixeli.e.2b

Acolordepthof4bitswouldbe2timesitself4times:2x2x2x2=16colors

Acolordepthofof8bitswouldbe2timesitself8times:

2x2x2x2x2x2x2x2=256colors.

Acolordepthofof24bitswouldbe2timesitself24times:

2x2x2x2x2x2x2x2x2x2x2x2x

2x2x2x2x2x2x2x2x2x2x2x2=16,777,216colors


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In

case

of

black

and

white

and

grey

scale

images,

the

three

primarieshavethesamevalue.Blackandwhiteimage

requiresonlyonebitperpixel,0representingblackand1

representingwhite.Greyscaleiscodedwith8bitsper

ixeltoallowatotalof256intensit of re levels. InRGBcolourmodel,thecolourisrepresentedbycolour

intensityoritsmix,whereas,inCMYKcolourmodel,the

co our sm xe npropor ons. .g.re co ormay e

composedof14%cyan,100%magenta,99%yellowand

3%black.


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RGB

true

color

would

have

a

24

bit

color

depth

and

CMYK

truecolorwouldhavea32bitcolordepth(8bitsper

colour)

CMYKtruecolourwouldhave256x256x256possible

.

colourspaceorgamutthanRGB.www.sketchpad.net/basics4.htm#gamut


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Low

storage

space

is

required

for

this

format.

Pixels

do

not

codecoloursdirectly.Theyrefertoatablewherecolour

valuerelatedtothatpixelisstored.

Thesecolourvaluesforma colourmap fortheimage.

referredtoasthe8bitformat.


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0

1

.

.

.

r g b

.8 bit pixel value

.

.255

24 bits


(8 bits per primary)

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Colours

derived

from

a

palette.

These

are

restricted

in

numbersandhencedonotproduceimagesasrealisticasit

canbeonusingRGBorCMYKmodel.

Thistypeofcolorisknownas"IndexedColor"because

whichareusedbythecomputertoidentifyeachcolor

Somefileformatsrestrictthenumberofcolorstofewerthan256.TheGIFformat hasacolordepthof8bitsper

pixelorless.GIFfilesuseindexedcolorandallowa

maximumof256colors.TIFFfilescanbestoredasindexed

colorortruecolor.


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Grayscale

images

have

a

maximum

color

depth

of

8

bits.

WhendefiningshadesofgrayintermsofRGB,eachofthe

3red,greenandbluecomponentsmustbeequaltoeach

other.ExamplesofgraysareR=192G=192B=192,and

R=128G=128B=128.

Sinceallthreecomponentsmustbeequalforanyshadeofgraythereareonly256possiblecombinations.


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black and white

1 bit colour: 2 colour palette:

blue and white


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4 bit color: 16 colour palette:

Windows 16 colour palette

use or screen grap cs


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8 bit color: 256 color palette:

8 bit grayscale: 256 shade grayscale palette:


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24 bit color: (No palette used)


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HSL Hue Saturation Li htness

Alternatesystems

HSIandHSB,whereIstandsforintensityandBstandsforbrightness

HSV Hue,Saturat on,Va ue

BothHSLandHSVdescribecolorsaspointsinacylinder

atthetopwithneutralcoloursbetweenthem,whereangle

aroundtheaxiscorrespondstohue,distancefromtheaxis

u , x

correspondstolightness,value,orbrightness.


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graphicsapplications.

HSVColourWheel

Thehueisrepresentedbyacircularregion

A

separate

triangular

region

may

be

used

to

represent

saturationandvalue.

Typically,theverticalaxisofthetriangleindicates, .

Inthisway,acolorcanbechosenbyfirstpickingthehue

fromthecircularregion,thenselectingthedesired

saturationandvaluefromthetriangularregion.


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HSVColourCone 3Dinnature

Thesaturationisrepresente yt e

distancefromthecenterof

acircularcrosssectionofHSV Colour Cone thecone,andthevalueis

thedistancefromthe

pointedendofthecone.

Some

representations

use

ahexagonalcone,or

hexcone insteadofa

circularcone


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HSVColourC linder Mostappropriatefor

mathematicalmodelling

Thenumberofvisuallydistinctsaturationlevels

valueapproachesblack

Theconstraintsofprecision,coupledwiththelimitations

ofhumancolorperception,

maketheconevisualization

morepractical.


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Doubleconeorsphere White at to black at

Invertedconeofcolour Black at the bottom and

bottom,andfullysaturated

colours aroundtheedgeof

fullysaturatedcolours

aroundthecircleandatthe

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TheSaturationcomponentalwaysgoesfromfully

Itgoesfromsaturatedcolortowhite

saturatedcolortothe

equivalentgray Vcomponentonlygoes

halfway,fromblackto

range,fromblacktowhite

throughcolour hue Traditionallymorecommon

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18,

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Applications TheCSS3specification

Applications AppleMacOSX systemcolor

Inkscape (startingfromversion0.42)

Macromedia Studio

picker(hasacolordiskfor

H/SandasliderforV)

Xara Xtreme

MicrosoftWindows systemcolorpicker(including

Microsoft Paint

Paint.NET (hasacolordiskforH/SandasliderforV)

Adobe ra hic a lications

PaintShopPro ImageMagick

(Illustrator,

Photoshop,

and

others)

PBMa InfoPro

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Pixelimageeditor (startingfromBeta5)

Pixia

Bryce

TheGIMP (HSVforcolorselection,HSLforimagecolora justment

Paint.NET (HSVforcolorselection,HSLforimagecolor

Photoshop (HSVforcolorselection,HSLforimagecoloradjustment)

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18,

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Letr b 0 1 bethered reen andbluecoordinates respectively,ofacolorinRGBspace.

Letmaxbethegreatestofr,g,andb,andmintheleast.

Tofindthehueangleh [0,360]foreitherHSLorHSVspace,compute:

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Tofindsaturationandli htnesss l 0 1 forHSLs ace compute:

Thevaluesfors andvofanHSVcoloraredefinedasfollows:

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18,

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(h normalizedtobeintherange[0,1))

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Rastogi 74

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Com uteeachcolorcom onentColor ofthevector Color ColorG,ColorB)=(r,g,b),


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RGB HSL HSV Result

1 0 0 0 1 0.5 0 1 1

(0.5,1,0.5) (120,1,0.75) (120,0.5,1)

(0,0,0.5) (240,1,0.25) (240,1,0.5)


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,

Zhigang andRoy,0624 A itiona Rea ing Compi e materia


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